Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2006

Finish Coat Over Zinc Chromate Primer

Q: I'm building an aircraft using Tempo zinc chromate primer over the 6061-T6 aluminium. What type of finish coat should I use that is compatable with zinc chromate primer? 

Here is information off the aerosol can which I hope will be of help:

Aviation Zinc Chromate Primer A7-6889 Yellow

Resin System: Alkyd Enamel

Federal Specification:

    TTP-1757A

    Mil-P-6889A

    Type 1 Mil-P-8585A

Resistance:

    Heat - 250°F

    Abrasion - good

    Adhesion - Excellent

    Corrosion - Excellent

Dry Time:

    Tack free - 15 to 30 minutes

    Fully dry - 2 hrs

    Recoat after two hours

Thanks for any assistance that you can give me.

A: You should use an alkyd or equivalent resin top coat, such as  an acrylic modified alkyd, or a silicone alkyd.  Unfortunately, the Tempo primer is unlikely to be compatible with a more durable topcoat, such as a two-component polyurethane.

Best wishes,

Ron Joseph